1 Field of the Invention
The invention relates to a method for determining the yaw velocity of a vehicle, in particular for adaptive driving-speed control, from wheel speeds measured by wheel-speed sensors on a right and a left non-driven wheel, wherein the yaw velocity of the vehicle is determined from a comparison of the measurements of the right wheel speed and the left wheel speed.
A system for controlling the driving stability of a motor vehicle is known from German Patent DE 44 36 162 C1, corresponding to U.S. patent application Ser. No. 08/837,241, filed Apr. 10, 1997. In that system, a control device is supplied not only with the wheel speeds measured by sensors, in order to control the brake pressure applied to the individual wheels on the basis thereof, but the control device also receives further signals from a steering-angle sensor and a yaw-velocity sensor, in order to keep the driving condition of the motor vehicle stable. In that context, it is also known to determine the yaw velocity, that is to say the rotation of the vehicle about the vertical axis, not in a sensor but instead by computation and specifically, for example, from the wheel speeds of the two front or rear wheels, or from the steering-wheel angle and a wheel speed.
Mathematical derivations for the steering-wheel angle, the yaw velocity and further functions in the case of driving a vehicle steadily in a circle at a constant radius with a constant driving speed are presented in a publication entitled "Dynamik der Kraftfahrzeuge"[Motor Vehicle Dynamics] by M. Mitschke, Vol. C, Fahrverhalten [Handling], 2nd Ed., Springer-Verlag, pp. 31-39. The functions are determined on one hand from vehicle data, such as mass m and wheelbase, l and on the other hand from steering data, such as steering angle and steering ratio. Those derivations also disclose the combination of a series of vehicle and steering data into a "characteristic driving speed" v.sub.ch. It is often not possible to determine the yaw velocity with the high accuracy often desired by using the equations given in the literature. Indeed, the tire pressure as well as the tire wear may vary on the different wheels. Furthermore, the handling may be affected by crosswind and by steering-angle corrections, for example in the case of a cambered road.
If it is desired to determine even low yaw velocities with high accuracy, then that is usually performed with yaw-velocity sensors as have been developed for aircraft navigation. Sensors of that type are expensive and are also sensitive to temperature, usually exhibiting a temperature drift of up to 1.degree./s.